1. Field of the Invention
The present invention relates to a sheet feeder of a corrugated paperboard box making machine for subjecting a sheet-shaped corrugated paperboard sheet to printing, creasing, slotting, and other processing and, more particularly, to a sheet feeder of a corrugated paperboard box making machine provided with a feed roll for feeding downstream corrugated paperboard sheets fed one by one from a stack of corrugated paperboard sheets on a sheet feed table.
2. Related Art
In general, a corrugated paperboard box making machine includes, from upstream to downstream, a sheet feeder for feeding various types of corrugated paperboard sheets, a printer for printing on a corrugated paperboard sheet fed thereto, a creaser-Blotter device for creasing and slotting a corrugated paperboard sheet to enable folding the sheet into a box shape, a die cut device for punching to form hand holes, and others. The sheet feeder is provided with feed rolls in upper and lower opposite positions to nip and feed downstream a corrugated paperboard sheet fed one by one from corrugated paperboard sheets stacked on a sheet feed table. The feed rolls are placed to extend in a direction perpendicular to a feeding direction of the corrugated paperboard sheets so as to allow a corrugated paperboard sheet having a maximum width among various types of corrugated paperboard sheets to pass between the feed rolls.
This pair of feed rolls is pivotally supported, at respective both ends in an axial direction, by a main unit and is rotated at high speed while nipping or pinching a corrugated paperboard sheet, fed between them, from above and below and in frictional contact with the corrugated paperboard sheet. Accordingly, each of the intermittently fed corrugated paperboard sheets strikes the feed rolls and then gets nipped between the feed rolls. Thus these feed rolls repeatedly receive a large impact force. This impact force causes a central part of each feed roll in the axial direction to be bent or warped in a direction to open a gap when the corrugated paperboard sheet passes between the rolls. After the corrugated paperboard sheet passes through the gap, the feed rolls are warped back to an original form. This warping vibration is repeated at high speed. If the feed rolls vibrate with large amplitude, some problems would occur; for example, scratches or indentations are generated on the surfaces of corrugated paperboard sheets and/or the feeding speed of the corrugated paperboard sheets varies.
Meanwhile, it is necessary to feed various types of corrugated paperboard sheets different in width, length in a feeding direction, thickness, flute shape, and others to the corrugated paperboard box making machine. Therefore, the sheet feeder is provided with an adjusting mechanism for adjusting a gap between the upper and lower feed rolls according to differences in thickness, flute shape, and so on of a corrugated paperboard sheet to be fed (e.g., see Patent Document 1).
The adjusting mechanism in Patent Document 1 is a mechanism in which an upper one of upper and lower feed rolls is rotatably attached to a main unit and a lower one is rotatably supported by an eccentric bearing case placed eccentrically with respect to an axis of the lower roll. This bearing case is rotatably attached to the main unit, so that the bearing case is rotated to adjust a gap between the upper and lower feed rolls.
In this case, since the upper roll is attached rotatably to the main unit, a center backing roller may be provided in the main unit so as to contact with an outer peripheral surface of a central part of the upper roll in the axial direction as mentioned above to reduce a bent or warped amount of the upper roll.